1. Field of the Invention
The present invention relates to a high pressure gas-operated setting tool including a piston guide, a driving piston displaceable in the piston guide and having a stem and a head, and a return member surrounding the stem and arranged between a stop, which is provided on the piston guide and faces in a direction opposite to a setting direction, and a front, in the setting direction, end face of the head.
2. Background of the Invention
For driving nail-shaped attachment members in hard structural components formed of cement, rock, steel and the like, high pressure gas-operated setting tools are used. In the preferred type of such setting tools, which are presently widely used, and from the safety point of view, the high pressure gas acts on a driving piston which acts on the driven attachment members. While those tools have certain advantages, on one hand, they also have a drawback, on the other hand, which consists in that after each driving-in cycle, the driving piston need be returned into its initial position. Because of this, for many years, return members for the driving pistons have been used. German publication DE-OS1 939 801 discloses an explosive powder charge-operated setting tool in which the driving piston is returned in its initial position after each driving-in cycle with a return member. The return member is formed as an elastic sleeve surrounding the piston stem and extending between a stop, provided on the piston guide and facing in a direction opposite to the setting direction, and a front, in the setting direction, end face of the piston head.
The elastic sleeve is surrounded by a hollow cylindrical free space so that the sleeve can expand radially when it is axially compressed. When the sleeve is compressed, the sleeve material becomes also compressed. This results in a substantial heat generation which leads to a premature changes in and to a high wear of the material. When the free space is used up, i.e., when the sleeve cannot expand radially any more, a further axial compression of the sleeve becomes impossible. The sleeve, which is disclosed in DE-OS 1 939 801 and is shown in FIG. 1 of this publication, at most, can be compressed to a length corresponding to about 800 of the original length of the return member. This small axial displacement of the drive piston is particularly disadvantageous when nail-shaped attachment member having a substantial length must be driven into a structural component.
Accordingly, an object of the present invention is to provide a high pressure gas-operated setting tool the return element of which can be economically produced, which would insure an adequate return displacement of the drive piston in its initial position after each driving-in cycle, which would have a small weight, and which would be compressible to more than half of its initial length.